What armored vehicle did Leonardo da Vinci design for four crew members?

Leonardo da Vinci designed a fighting vehicle, an armored machine often described as an early tank concept.

The design appears in Leonardo’s notebooks from the late 15th century. It resembles a conical, turtle-like armored shell mounted on wheels, with weapons projecting around its perimeter. Inside, men would turn cranks to drive the wheels and move the vehicle across the battlefield.

Popular accounts sometimes say Leonardo deliberately included a gearing error so that an enemy would not be able to build the machine. Historians and engineers have debated whether the apparent problem was intentional, accidental, or simply a feature of an incomplete drawing. The vehicle was never built for Renaissance warfare.

Calling it a tank is useful as a comparison, not as a claim that it was a modern armored tank. Leonardo’s concept lacked an engine, suspension, and practical steering system, but it combined armor, mobility, and onboard weapons in a strikingly modern way.